Combustion of air-fuel mixtures at the cylinders of a vehicle engine generates torque to power a propulsion of the vehicle. The process of combustion produces exhaust gas that is evolved at the cylinders and channeled into an exhaust management system of the vehicle. The exhaust gas may be composed of a mixture of by-products including nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons, and particulate matter. Release of such materials into the atmosphere is undesirable and current exhaust management systems are configured to remove these chemicals from the exhaust gas prior to emission.
Treatment of exhaust gas may include removal of NOx, CO, and hydrocarbons by one or more three-way catalytic converters (TWCs) and particulate matter by a gas particulate filter (GPFs), where both devices are positioned between an exhaust manifold of the engine and an outlet of an exhaust pipe of the vehicle. The TWC and GPF are effective systems for removal of combustion by-products but may become degraded over time. For example, components of the exhaust system that are frequently exposed to outdoor elements, such as the TWC housing and the exhaust pipe, and temperature changes, such as the exhaust manifold, may rust or crack, leading to leakage of untreated exhaust gas. In addition, accumulation of particulate matter in gas flow pathways of the exhaust system may occur, resulting in blockages that degrade engine performance due to back pressure in the exhaust system. Thus, methods to diagnose leaks and blockages in the exhaust system soon after the leaks and blockages are formed may allow the system to be repaired before degradation increases and adversely affects engine performance.
Attempts to address detection of degradation to the exhaust system include operating an electrical supercharger to diagnose vehicle components. One example approach is shown by Bauerle et al. in U.S. Pat. No. 6,688,104. Therein, an electrical supercharger is activated after a vehicle is stopped and diagnostic methods to assess an intake manifold and an exhaust system of the vehicle are conducted. For example, an exhaust gas recirculation (EGR) valve operation may be evaluated based on measured changes in pressure or correct functioning of an exhaust temperature sensor may be determined by comparing a temperature signal to a pre-set reduction in temperature resulting from a cooling effect of the active electrical supercharger.
However, the inventors herein have recognized potential issues with such systems. As one example, the method of U.S. Pat. No. 6,688,104 does not include monitoring the exhaust system for leaks or blockages. Degradation of specific exhaust components such as the EGR valve or exhaust temperature sensor may not be indicative of leak formation in the exhaust manifold. If the diagnosed parts are deemed to be in satisfactory condition in spite of the presence of a source of degradation, operation of the vehicle may proceed with the leak or blockage unnoticed until degradation of other exhaust system elements or decreased engine performance occurs.
In one example, the issues described above may be addressed by a method for, upon engine shutdown, operating an electric turbocharger to draw air into an exhaust system and indicating degradation of the exhaust system based on a comparison of a pressure in the exhaust system measured during operating the electric turbocharger to a threshold pressure that is based on a barometric pressure. In this way, leaks and blockages in an exhaust system may be detected using elements already present in a vehicle engine system.
As one example, a throttle and one or more cylinder valves may be closed to create a closed system upstream of a turbine of an electric turbocharger. The electric turbocharger may be actuated after the engine is turned off and spun in a direction opposite of a direction when the turbocharger is operated when the engine is on (e.g., a reverse direction). The reverse spinning of the turbine may pull air, in reverse through an exhaust passage and into the exhaust manifold. A comparison of the pressure in the exhaust manifold, while running the turbocharger in reverse, to a threshold pressure that is determined based on barometric pressure is conducted to determine if a leak is present. In another example, the electric turbocharger may be spun in a forward direction, opposite of the reverse direction, with the engine off and throttle and the intake and exhaust valves of the cylinders in open positions to allow airflow through the cylinders and into the exhaust system. An exhaust tuning valve in an exhaust pipe may be closed to restrict air flow out of the exhaust pipe, allowing pressure to accumulate when air is pumped into the exhaust pipe, from upstream to downstream of the turbine. Pressures in the exhaust pipe and exhaust manifold may be measured and compared to a set of thresholds calculated as functions of barometric pressure to determine if the exhaust system is degraded.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.